But there are also things that can be subtracted, but not added. The simplest example is dates. You can subtract two dates to get the time interval between them, but you cannot add two dates. It doesn’t make sense to ask what today plus tomorrow is. You could try to add the numeric values corresponding to the dates and convert the answer back to a date, but the result would depend on whether you count from the start of the Common Era, the Unix epoch, or something else.

While adding two dates is not possible, it is possible to add a time interval to a date («five days from today»). This suggests that we should not confound dates and time intervals — they are different types of values.

Finding out current times in other places
Correlating times in different zones with each other
Calculating time spans and durations for scheduling, time-sheets and similar

The output is usually in ISO 8601 format. The parsing tries to be slightly cleverer, but basically sticks to ISO 8601 text formats. No major effort has been put into trying to understand all variants of date formats, but major pain points have hopefully been addressed (such as accepting AM/PM time designations).

An image kernel is a small matrix used to apply effects like the ones you might find in Photoshop or Gimp, such as blurring, sharpening, outlining or embossing. They're also used in machine learning for 'feature extraction', a technique for determining the most important portions of an image. In this context the process is referred to more generally as "convolution" (see: convolutional neural networks.)